To flow liquids in pipes, energy must be expended to overcome frictional losses. This energy is extracted from the liquid pressure, which decreases along the pipe in the direction of flow. For a fixed pipe diameter, these pressure drops increase with increasing flow rate until a maximum is reached when the pressure drop along the pipe equals the supply pressure at the beginning of the pipe. When flow in the pipe is turbulent (flow Reynolds number=mean fluid velocity.times.pipe diameter.div.fluid kinematic viscosity greater than about 2000) this maximum flow rate can be increased by the addition of small amounts of certain high molecular weight linear polymers to the liquid. These polymers interact with the turbulent flow processes and reduce frictional pressure losses such that the pressure drop for a given flow rate is less, or the maximum flow rate for a given pressure drop is larger. This phenomenon is commonly called drag reduction. It has been successfully used in commercial oil pipelines, fire hoses and storm sewers to increase the flow capacities of existing systems. It can also be used to reduce supply pressures, pumping costs, and/or pipe diameters for given flow capacities.
High molecular weight hydrocarbon soluble polymers such as polyisobutylene, polystyrene, and several poly alpha-olefins have been demonstrated to reduce drag in turbulent flows of hydrocarbon liquids. Generally, the drag reduction effectiveness of these polymers improves with increasing molecular weight; however, the tendency for the polymers to permanently degrade via molecular scission within pumps or turbulent piperflows also increases with increasing polymer molecular weight. This invention discloses efficient drag reduction in hydrocarbon liquids resulting from a novel class of interacting polymers which interact via a coordination chemistry-type mechanism. For example a terpolymer of a metal (i.e. transition metal) neutralized styrene sulfonate can interact with styrenevinylpyridine monomer units chemically attached to the same polymer chain molecule. Such coordination-type interacting polymers can provide improved drag reduction via formation of higher molecular weight entitles or even a polymeric networks rather than by high molecular weight. Consequently such larger molecular weight structures of networks can be less sensitive to flow degradation due to the ability of the coordination-type bonding to absorb energy from the fluid itself in a reversible manner. These bonds will break and subsequently reform in a flowing fluid, reducing the stress on an individual chain and, therefore, preventing a substantial and permanent deterioration in the molecular weight, especially as compared to its non-associating or non-coordinating counterpart.
This invention teaches that a polyampholyte can be effective as a drag-reducing agent for hydrocarbon solutions. Such a polyampholyte can behave like a higher molecular weight polymer which is normally needed for drag reduction. One can, therefore, form a network from polymers that are relatively low in molecular weight and potentially reduced sensitivity to backbone degradation under flow. Moreover, the network cannot be completely destroyed by adding a small amount of a polar cosolvent additive, such as an alcohol or other polar additives, which normally strongly interferes with the interaction mechanism.
In recent years there has been a renewed interest in the physical properties of polymeric complexes (i.e., polyampholytes). These materials have a variety of interesting properties since, for all practical purposes, the cations and anions are chemically attached to the molecular structure of the macromolecules. The counterions of any type are not free to move into the bulk solution as found in classical polyelectrolytes. In addition, it is generally assumed that each individual polymer chain possesses an equal number of cations and anions.
Salamone, et al., the University of Lowell (Massachusetts) are investigating ampholytic polymers as a part of their research program. They have studied the solution properties of divinylic cationic-anionic monomer pairs and also cationic-anionic monomer pairs with a neutral comonomer (J. Poly. Sci. A1, 18 2983 [1980]) which can be incorporated into the ampholytic macromolecular structure through both solution or emulsion polymerization schemes. Apparently, other neutral vinylic monomers (i.e., acrylamide) were also polymerized (Gordon Research Conference--1981); but as of the present time reports of this work have not been published in the scientific literature. However, in all of Salamone's work detailed descriptions of his synthesis is reported. In all instances the polymerization of the anionic-cationic monomeric species occurred via "ion-pair comonomers that have no nonpolymerizable counterions present" (J. Poly. Sci.-Letters, 15, 487 [1977]). Apparently, the physical and chemical properties of these ion-pair comonomers are different than the individual ions (J. Poly. Sci.-Letters, 15, 487 (1977).
Polymeric materials are generally considered useful as viscosification agents when dissolved in an appropriate solvent system. The major reason for this viscosity enhancement is due to the very large dimensions of the individual polymer chain, as compared to the dimension of the single solvent molecules. Any increase in the size of the polymer chain will produce a corresponding enhancement in the viscosity of the solution. This effect is maximized when the polymer is dissolved in a "good" solvent. Therefore, in general, a hydrocarbon soluble polymer is useful for thickening hydrocarbon solvents, while a water soluble polymer is appropriate for increasing the viscosity of aqueous systems. With regard to nonaqueous solutions, hydrocarbon based solvent soluble nonionic polymers and low charge density sulfonated isomers are quite useful in this regard and are commonly used materials. However, the solution properties of the former family of materials are controlled primarily through modification of the molecular weight of the polymer and through changes in the level of dissolved polymer. These materials become especially effective at concentrations where the individual polymer chains begin to overlap. This "transition" is commonly referred to in the literature as the chain overlap concentration, or simply C*. It should be noted that in most nonionic polymers of commercial interest a relatively large amount of polymer is required prior to reaching C*. Therefore, this approach is undesirable from an economic viewpoint. Moreover, the rheological properties of many of these nonionic systems have been published. The results of these studies show that, in general, these solutions are shear thinning over all shear rates investigated.
With regard to lightly sulfonated ionomers, the viscosification efficiency of these materials are primarily controlled through formation of an ionically-linked network structure. As long as this network structure remains in tact the sulfonated ionomers possess outstanding viscosity characteristics, such as improved thickening efficiency, especially as compared to its nonionic counterpart, and shear thickening. However, these ionic interactions can be dramatically weakened and even completely eliminated if a polar cosolvent, such as an alcohol or an amine, is dissolved into the solution system. However, it should be noted that a polar cosolvent is required in a number of these materials for solvation to occur. Typically, insolubility in xylene (i.e., inability to form a homogeneous single phase solution) occurs in a low charge density sulfonate ionomer solution if the sulfonation level is greater than approximately 1.0 mole percent. A direct consequence of the addition of these polar cosolvents is a corresponding reduction in solution properties, such as thickening efficiency and drag reduction. For example, shear thickening is completely eliminated or sharply reduced in magnitude at relatively low levels of methanol.
This invention teaches that a low charge density sulfonate-containing polyampholytes (example: styrene-styrene sulfonate-4 vinylpyridine terpolymers) are readily soluble in single component, nonaqueous solvents. A polar cosolvent is not always required for solvation to take place. Due, in part, to this solubility characteristic, these materials are useful in drag reduction applications.